Device for measuring distance of travel by a projectile

ABSTRACT

The distance traversed by a spin-stabilized projectile is determined by a pendulum attached inside the fuze of the projectile so that each complete swing of the pendulum is equal or proportional to one complete revolution of the spinning shell. The distance traversed by the projectile is determined from reading of the number of complete cycles (frequency) made by the pendulum which, in turn, is equal to the number of revolutions of the spinning shell.

Mute States tet 1 1111 3,53,862

Cole Dec. 110, 1974 DEVICE FOR MEASURING DISTANCE OF 1,992,278 2/1935Aliquo 102/83 TRAVEL BY A PROJECTXLE 3,297,948 1/1967 Kohler 102/70.2 R3,353,487 11/1967 Perryman l02/70.2 R [75] Inventor: Lewis C. Cole,Chester, NJ.

[73] Assignee: The United States of America as primary Examiner samuelFeinberg represented the Secretary of the Assistant Examiner-C. T.Jordan Army, Washington, DC. Attorney, Agent, or FirmEdward J. Kelly;Herbert 22 Filed; 23 1973 Berl; A. V1ctor Erkklla [21] Appl. No.:336,663

Related US. Application Data Continuation-impart of Ser. No. 159,374,July 2, 1971, abandoned US. Cl. 102/70.2 R, 102/70 R lint. Cl F426 9/00,F420 ll/OO Field of Search lO2/70.2 R, 70 R, 79, 82,

References Cited UNITED STATES PATENTS l0/l924 Hawkins 102/83 [5 7]ABSTRACT The distance traversed by a spimstabilized projectile isdetermined by a pendulum attached inside the fuze of the projectile sothat each complete swing of the pendulum is equal or proportional to onecomplete revolution of the spinning shell. The distance traversed by theprojectile is determined from reading of the number of complete cycles(frequency) made by the pendulum which, in turn, is equal to the numberof revolutions of the spinning shell.

6 Claims, 5 Drawing Figures PAIENTEU mu: 1 0mm SETTER OUTPUT COUNTERPENDULUM DEVICE FOR MEASURING DISTANCE OF TRAVEL BY A PROJECTILE Theinvention described herein may be manufactured, used and licensed by orfor the Government for governmental purposes without the payment to meof any royalties thereon.

This is a continuation-in-part of Application Ser. No. 159,374, filedJuly 2, 1971, now abandoned.

BACKGROUND OF THE INVENTION 1. Prior Art The devices which haveheretofore been employed in a projectile to determine the distancetraversed by the projectile have been of the type which measure thedistance in accordance with elementary laws of physics. According tothese well-established principles, the distance traversed by aprojectile is the product of the velocity of the projectile and its timeof travel and may be represented by the following equation:

where s is the distance, in feet, traversed by the projectile, v is thevelocity of the projectile in feet per second, and t is the time, inseconds, required for the projectile to travel the distance s.

The disadvantages of the devices which are based upon this method ofdetermination of the distance traversed by a projectile are immediatelyapparent from an inspection of the foregoing equation since the velocityof the projectile is not constant but rather, it is an average valuewhich is affected by environmental conditions which may varyconsiderably from one time to another and from one location to another.Accordingly the distance measured using the devices which haveheretofore been employed is necessarily an estimation, at best, and itis extremely difficult to preselect the exact distance which aprojectile is required to travel. The uncertainties and the inherentinaccuracies which are associated with this method or means of measuringsuch distances are obvious limitations in those instances where accuratemeasurements are required and/or when the projectile is required totravel a predetermined distance with a high degree of accuracy.Accordingly, the need for a device or means which would permit accuratemeasurement of such distances and/or which would permit the selection ofthe distance of travel of a projectile in advance is readily apparentand highly significant particularly in the armament field.

2. Summary of the Invention This invention contemplates providing ameans for accurate determination of the distance traversed by'aprojectile.

In one aspect, the present invention relates to a device which iscapable of measuring the distance traversed by a projectile from thenumber of revolutions of the spinning shell of the projectile.

In another aspect, the present invention is directed to a device whichpermits the selection of a predetermined distance which a projectile isdesired to travel.

In still another aspect, this invention is concerned with providing sucha device for projectiles wherein the function of the device isunaffected by the velocity of the projectile.

These and other aspects of this invention will be more clearlycomprehended from the following de- BRIEF DESCRIPTION OF THE DRAWINGSThe understanding of the present invention will be facilitated byreference to the accompanying drawings wherein like numerals areemployed to designate like parts. In the drawings:

FIG. I is a side view, partly in section, of a fuze embodying theprinciples of this invention;

FIG. 2 is a side view, partly in section, of a projectile containing thefuze shown in FIG. 1, and

FIG. 3 is a diagram illustrating the mathematical relationship betweenthe frequency of the pendulum swings and the revolutions of theprojectile.

FIG. 4 is a blocked diagram illustrating one method of the operation ofthe device of this invention.

FIG. 5 is a diagrammatic view of a fuze of this invention containing adouble ended pendulum.

DETAILED DESCRIPTION OF THE INVENTION It has now been unexpectedlydiscovered that by incorporating a novel device (to be hereinafterdescribed) into the fuze of a projectile, the distance traversed by theprojectile can be measured accurately from the number of revolutions ofthe spinning shell of the projectile. It has further been discoveredthat the device employed herein can be preset for a predetermineddistance of travel by the projectile with high degree of accuracy.

Basically, the principles of this invention and the device employedherein are applicable to the so-called spin-stabilization projectiles ascompared to the other types of projectiles which are commonly known inthe art as fin-stabilized projectiles. Examples of spinstabilizedprojectiles for which the device of this invention is particularlysuitable include guns of various calibers, rifles, etc., and similararmaments, whereas finstabilized projectiles generally include darts,mortar shells and the like. The device of this invention (a pendulum orthe like) is simply incorporated into the fuze of the projectile so thatthe frequency of the pendulum is determined by the frequency of thespinning projectile as will be hereinafter described in further detail.

Referring now to the drawings and particularly to FIGS. 1 and 2, thereis shown a fuze I mounted in the forward part of projectile 3 in theusual manner as shown in FIG. 2 and the direction of the revolutions ofthe spinning shell of the projectile is indicated by the curved arrowsaround its longitudinal axis.

Also shown in FIGS. 1 and 2 is a pendulum consisting of a swing arm 5,one end of which is attached to the center of the fuze by a pin 7 or byany other suitable means and the other end of which is integrallyattached to a ballor disc-like object 9. This will permit measurement ofthe distance traversed by the projectile from a reading of the frequencyof the pendulum since the frequency of the pendulum (f,,) is equal tothe frequency of the shell (f Stating it differently, each completeswing cycle of the pendulum as employed herein is equal or proportionalto one complete revolution of the fuze. This one-to-one relationship canbe demonstrated mathematically in connection with FIG. 3 by thefollowing equations:

wherein f 11) frequency of the pendulum L length of pendulum gacceleration due to spin force field. For small angle 6 r the radialdistance from the end of the pendulum to the spin axis,

w spin of round in radians per second,

f frequency of spinning round in revolutions per second. It can be seenfrom the figure that for small angle 0, L r and the force field out dueto spin can be given by g =r W2 which is equal to r times the'quantity(271-11 Substituting for L and g in the equation forfl, it cari be seenthat the equation reduces to the following:

From the above relationship it can be seen that the frequency of thependulum is equal to the frequency of the projectile, that is, thependulum makes one complete swing cycle for each revolution of theprojectile. For a larger angle 0, a proportionality between pendulumcycles/projectile revolutions can be calculated. Thus, for example, itcan be shown by a rigorous mathematical analysis that when 1, 99.997pendulum cycles equal I00 projectile revolutions, while when 0 =30, 97pendulum cycles equal 100 projectile revolutions. This can becompensated by suitably adjusting the number of revolutions preselectedby the setter.

When a projectile containing a fuze of the present invention is fired,the resultant setback force compels the pendulum to the start position,which is the start of the swing, as shown in FIG. 1. The instant theprojectile leaves the gun muzzle, the setback force drops to zero, as iswell known according to Newtons law F m a, since acceleration (a) iszero whereby the (setback) force (F) on the projectile mass (m) is alsozero. Simultaneously, the pendulum, thus free of setback force, beginsto swing in response to the centrifugal force generated by the spin ofthe projectile, which at that instant is at a maximum, and swings in alongitudinal plane with the pivot point at pin 7 on the spin axis of thefuze,

performing one complete swing cycle, i.e., p to p and back to p, foreach revolution of the projectile, as mathematically shown above withreference to FIG. 3. Accordingly, since the setback force drops to zeroand the projectile spin rate is essentially maximum at the instant theprojectile exits from the gun muzzle, the invention provides aninstantaneous attainment of the one to one relationship between pendulumoscillation cycles to projectile revolutions, and hence achieves anaccurate count of the distance by the number of projectile revolutions.Thus, from the number of revolutions that the projectile has made, ascounted by the pendulum cycles, the distance traversed by the projectilecan be readily determined, since the distance per each revolution of thespinning projectile is the product of the twist of the projectile timesits caliber and is independent of the initial projectile velocity, as isknow in the art, viz.

distance/revolution caliber/twist For example. for a 105 mm round firedin a gun having a l in twist, the projectile can be expected to travel6.9 feet per revolution.

For measuring short distances, i.e., when there is a negligible changein projectile velocity to spin rate, the

distance traversed is determined by the caliber and rifling twist. Forlong distances, when this relationship does not hold, it will benecessary to establish experimentally a ratio of the number ofprojectile revolutions to the position (distance) of the projectile toprovide the necessary relationship, e.g., as would be used in a firingtable similar to that currently done with time fuz- While in thecentrifugal force field of the spinning projectile, the pendulum tendsto damp out, i.e., suffer a decrease of swing amplitude, due to frictionforces. This reduction of amplitude has a slight effect on the ratio ofpendulum cycles to projectile revolutions due to change in angle 0,which can be mathematically determined as noted above. If the pendulumdamps out too rapidly for the desired application, energy may be addedto compensate for loss in known manner, e.g., by a main spring orelectromagnetically, as used in clock mechanisms.

Thus, the novel pendulum arrangement for counting the number orprojectile revolutions provides a valuable advance in the art in that itis relatively simple and economical in construction, and automaticallycompensates for variations in muzzle velocity for short dis tances andalso tends to compensate for such error in long distance applications,thereby providing a fuze better adapted to battlefield conditions.

The frequency of the pendulum can be measured by any known means suchas, for example, by a photocell, electronically, or by mechanical meanssuch as, for example, a ratchet wheel of the type employed in pendulumclocks, and the like. In all cases, the means employed for reading thefrequency of the pendulum (and hence the number of revolutions of thespinning shell of the projectile) may be suitably connected to thependulum so-as to provide a convenient means for determining the numberof revolutions of the spinning shell of the projectile.

In operation, and in accordance with one embodiment of the invention,the pendulum is connected to a counter (not shown in FIGS. 1 and 2 butillustrated in block diagram in FIG. 4 for the sake of simplicity) whichrequires, say, (n) counts (revolutions) for activating the fuze. Thesetter shown in FIG. 4 is mechanically or electrically connected to thecounter and is designed to put in the compliment, i.e., (n-a) counts andthe pendulum is set to put in (a) counts. In a preferred embodiment, thependulum is employed in conjunction with a photoelectric cell counterconnected by electric circuits to a digital count totalizer (setter),which produces a current pulse for initiating the fuze when the counttotals the preselected number of counts (revolutions). In this casethere are two counts for each pendulum cycle per projectile revolution,since the pendulum arm cuts the light beam twice during one pendulumcycle, i.e., once when it swings from p to p and once .when it returnsfrom p to p (see FIG. 3). Accordingly,

While the present invention has heretofore been described with a certaindegree of particularity, it must be emphasized that the device describedherein and the principles of its operation are both susceptible ofvarious modifications and/or revisions without departing from the basiccharacter of this invention. For example, the device employed herein maybe employed in the socalled S&A (safety and arming) rotating a detonatorin line or in any other application where the frequency of the pendulumis proportional to the spin velocity of a spinning shell. This may beaccomplished by the use of the well-known Coriollos Force which wouldrotate a can, barrel, or any other similar device containing thependulum and the detonator.

While a single ended pendulum has been shown in FIGS. 1 and 2, anypendulum means can be employed for the purpose of this invention. Thus,a double ended pendulum 10, comprising a bar having equal weights 9 and9 attached at each end of swing arms 5 and 5' of said bar and mounted soas to pivot at its midpoint 7 corresponding to its center of gravity,may be utilized to reduce the effects of eccentric spin (where the pivotpoint is off the spin axis) as well as to minimize generally the forceson the pivot and thereby reduce the friction forces on the pendulum. Inall cases, the pendulum means is attached to the center (rotating axis)of the fuze mounted in the projectile and is connected to a mechanical,electronic or any other suitable means for reading the number offrequencies.

Hence, the device of this invention provides a convenient means forpresetting the distance a projectile is desired to travel. Since, as waspreviously mentioned, the function of the device is independent of thevelocity of the projectile, such distances can be preset and measuredindependently from changes in environmental conditions.

I wish it to be understood that I do not desire to be limited to theexact method and detail of construction described for obviousmodifications will occur to persons skilled in the art.

What is claimed is:

l. A device for determining the distance traversed by a spin-stabilizedprojectile having a spinning shell, which device comprises, incombination, a fuze element coaxially mounted in said projectile,pendulum means attached to said fuze element and adapted to oscillatetherein in response to the centrifugal force generated by said spinningshell so that the frequency of cycles of said pendulum means isproportional to the revolutions of said spinning shell of saidprojectile, and means for determining the frequency of oscillation ofsaid pendulum means.

2. A device as in claim 1 wherein said pendulum comprises a swing-armhaving two ends, one end being pivotably attached to the center of saidfuze element and the other end being attached to a discor ball-likeobject.

3. A device as in-claim 1 wherein the means for determining thefrequency of oscillation of said pendulum means comprises aphotoelectric cell.

4. A device as in claim 1, wherein the means for determining thefrequency of oscillation of said pendulum means comprises a ratchet orescape wheel.

5. A device as in claim 1, wherein the pendulum is a double endedpendulum.

6. A method for presetting the distance of traverse of a spin-stabilizedprojectile having a spinning shell and a fuze element which methodcomprises:

1. mounting in said fuze element a pendulum means adapted to oscillatetherein in response to the centrifugal force generated by said spinningshell so that the frequency of the oscillation cycles of said pendulummeans is proportional to the number of revolutions of said spinningshell of said spinstabilized projectile;

2. associating said pendulum means with a counting means for determiningthe frequency of oscillation of said pendulum means and adapted toactivate said fuze element at a predetermined number of oscillations ofsaid pendulum means;

3. connecting said counting means to a setting means;

and

4. adjusting the setting means to cause activation of said fuze elementat a predetermined number of oscillations of said pendulum meanscorresponding to the preset distance of traverse of said projectile.

1. A device for determining the distance traversed by a spinstabilizedprojectile having a spinning shell, which device comprises, incombination, a fuze element coaxially mounted in said projectile,pendulum means attached to said fuze element and adapted to oscillatetherein in response to the centrifugal force generated by said spinningshell so that the frequency of cycles of said pendulum means isproportional to the revolutions of said spinning shell of saidprojectile, and means for determining the frequency of oscillation ofsaid pendulum means.
 2. A device as in claim 1 wherein said pendulumcomprises a swing-arm having two ends, one end being pivotably attachedto the center of said fuze element and the other end being attached to adisc- or ball-like object.
 2. associating said pendulum means with acounting means for determining the frequency of oscillation of saidpendulum means and adapted to activate said fuze element at apredetermined number of oscillations of said pendulum means; 3.connecting said counting means to a setting means; and
 3. A device as inclaim 1 wherein the means for determining the frequency of oscillationof said pendulum means comprises a photoelectric cell.
 4. A device as inclaim 1, wherein the means for determining the frequency of oscillationof said pendulum means comprises a ratchet or escape wheel.
 4. adjustingthe setting means to cause activation of said fuze element at apredetermined number of oscillations of said pendulum meanscorresponding to the preset distance of traverse of said projectile. 5.A device as in claim 1, wherein the pendulum is a double ended pendulum.6. A method for presetting the distance of traverse of a spin-stabilizedprojectile having a spinning shell and a fuze element which methodcomprises: